In search of effective anti-HHV-6 agents

Synthesis and biological evaluation of novel rhodanine-based structures with antiviral activity towards HHV-6 virus

An increased awareness of diseases associated with Human herpesvirus 6 (HHV-6) infection or reactivation has resulted in a growing interest in the evaluation of the best treatment options available for the clinical management of HHV-6 disease. However, no compound has yet been approved exclusively for HHV-6 infection treatment. For this reason, the identification of anti-HHV6 compounds provides a valuable opportunity for developing efficient antiviral therapies. A possible target for antiviral drugs is the virus-cell fusion step. In this study, we synthetized potential fusion intermediates inhibitors based on the rhodanine structure. The obtained derivatives were tested for cytotoxicity and for antiviral activity in human cells infected with HHV6. Level of infection was monitored by viral DNA quantification at different time points up to 7 days post infection. Among the synthetized derivatives, 9e showed a significative inhibitory effect on viral replication that lasted over 7 days, probably attributable to the particular combination of hydrophilic and hydrophobic substituents to the rhodanine moiety. Our results support the use of these amphipathic fusion inhibitors for the treatment of HHV-6 infections.

A3- and A2B-fluorocorroles: synthesis, X-ray characterization and antiviral activity evaluation against human cytomegalovirus infection

Twenty-nine fluorinated corroles were prepared, spectroscopically characterized, and studied for their antiviral activity against human cytomegalovirus infection. Six corroles were also fully characterized by X-ray crystallography giving insights on their geometrical features. The halogenated corroles reported herein exhibit significantly improved antiviral activity over their non-halogenated counterparts and over nitro-corrole analogs previously reported. Full activity of thirteen A₃-corroles is achieved with four fluorine atoms present on the meso-phenyl ring reaching a selectivity index above 300. The maximum activity is achieved for A₂B-corroles with selectivity indexes above 400. We thus demonstrate that the fluorocorrole is a highly potent platform to synthesize a new generation of anti hCMV molecules.

A3- and A2B-nitrocorroles: synthesis and antiviral activity evaluation against human cytomegalovirus infection

Human cytomegalovirus (hCMV) is responsible for several pathologies impacting immunocompromised patients and can trigger life-threatening infection. Several antivirals are available and are used in the clinic, but hCMV resistant strains have appeared and patients have encountered therapeutic failure. Hence, there is a constant need for new best in class or first in class antiviral molecules. We have previously shown that nitrocorroles could be used as a potent anti-hCMV agent without acute toxicity in mice. They therefore represent an excellent platform to perform structure-activity relationship (SAR) studies and to increase efficiency or reduce toxicity. We have generated original A₂B- and A₃-substituted nitrocorroles and have discovered optimized compounds with selectivity indices above 200. These compounds are easily synthesized in only one to two-step reactions; they are up-scalable and cost efficient. They are therefore excellent candidates for hCMV therapies and they pave the way for a new generation of molecules.

Fatal outcome after reactivation of inherited chromosomally integrated HHV-6A (iciHHV-6A) transmitted through liver transplantation

HHV-6A and HHV-6B are found as inherited and chromosomally integrated forms (iciHHV-6A and -6B) into all germinal and somatic cells and vertically transmitted in a Mendelian manner in about 1% of the population. They were occasionally shown to be horizontally transmitted through hematopoietic stem cell transplantation. Here, we present a clinical case of horizontal transmission of iciHHV-6A from donor to recipient through liver transplantation. Molecular analysis performed on three viral genes (7.2 kb) in the recipient and donor samples supports transmission of iciHHV-6A from the graft. Transmission was followed by reactivation, with high viral loads in several compartments. The infection was uncontrollable, leading to severe disease and death, despite antiviral treatments and the absence of resistance mutations. This case highlights the fact that physicians should be aware of the possible horizontal transmission of iciHHV-6 and its consequences in case of reactivation in immunocompromised patients.

Human Herpesviruses 6A, 6B, and 7

Human roseoloviruses include three different species, human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7), genetically related to human cytomegalovirus. They exhibit a wide cell tropism in vivo and, like other herpesviruses, induce a lifelong latent infection in humans. In about 1% of the general population, HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6). Many active infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. They also may cause serious diseases, particularly in immunocompromised individuals, including hematopoietic stem-cell transplant (HSCT) and solid-organ transplant recipients, and acquired immunodeficiency syndrome (AIDS) patients. This opportunistic pathogenic role is formally established for HHV-6 infection and less clear for HHV-7. It mainly concerns the central-nervous system, bone marrow, lungs, gastrointestinal tract, skin, and liver. As the best example, HHV-6 causes both exanthema subitum, a benign disease associated with primary infection, and severe encephalitis associated with virus reactivations in HSCT recipients. Diagnosis using serologic and direct antigen-detection methods currently exhibits limitations. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time polymerase-chain reaction (PCR). The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active infections, but there is currently no consensus regarding the indications of treatment or specifics of drug administration. Numerous questions about HHV-6A, HHV-6B, HHV-7 are still pending, concerning in particular clinical impact and therapeutic options in immunocompromised patients.

Reactivation of Human Herpes Virus-6 After Pediatric Stem Cell Transplantation: Risk Factors, Onset, Clinical Symptoms and Association With Severity of Acute Graft-Versus-Host Disease

BACKGROUND AND METHODS

To study clinical symptoms, timing and consequences of human herpesvirus-6 (HHV-6) reactivation after pediatric allogeneic stem cell transplantation (SCT), HHV-6 was investigated by plasma polymerase chain reaction in a cohort of 106 pediatric SCT recipients.

RESULTS

HHV-6 viremia was detected post-SCT in 48% of the patients with a median time of onset at 20 days after SCT. In week 3 and 4 post-SCT, HHV-6 is the most common infectious agent detected. In up to 30% of the patients with fever of unknown origin, HHV-6 was the only detected infectious agent to explain fever. Patients transplanted with an unrelated donor or receiving serotherapy were at increased risk of HHV-6 reactivation. The onset of HHV-6 reactivation coincided with the appearance of lymphocytes and monocytes in peripheral blood. Treatment with alemtuzumab (MabCampath) delayed both lymphocyte and monocyte engraftment and, concomitantly, onset of HHV-6 reactivation was delayed in those cases. HHV-6 reactivation was not associated with an increased incidence of acute graft-versus-host disease (GvHD). However, progression to grade II-IV GvHD was in 9 of 10 patients associated with HHV-6 reactivation before GvHD (P = 0.006) and HHV-6 was the only infection with such an association.

CONCLUSIONS

HHV-6 frequently reactivates after pediatric SCT around the time of mononuclear cell engraftment and is associated with an increased severity of GvHD. HHV-6 may explain fever of unknown origin in 30% of the patients early after SCT. Assessment of HHV-6 reactivation in patients early after SCT can be instrumental for clinical decision making.

Laboratory and clinical aspects of human herpesvirus 6 infections

Human herpesvirus 6 (HHV-6) is a widespread betaherpesvirus which is genetically related to human cytomegalovirus (HCMV) and now encompasses two different species: HHV-6A and HHV-6B. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. As a noticeable difference with respect to other human herpesviruses, genomic HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6) in about 1% of the general population. Although it is infrequent, this may be a confounding factor for the diagnosis of active viral infection. The diagnosis of HHV-6 infection is performed by both serologic and direct methods. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time PCR. Many active HHV-6 infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. However, the virus may be the cause of serious diseases, particularly in immunocompromised individuals. As emblematic examples of HHV-6 pathogenicity, exanthema subitum, a benign disease of infancy, is associated with primary infection, whereas further virus reactivations can induce severe encephalitis cases, particularly in hematopoietic stem cell transplant recipients. Generally speaking, the formal demonstration of the causative role of HHV-6 in many acute and chronic human diseases is difficult due to the ubiquitous nature of the virus, chronicity of infection, existence of two distinct species, and limitations of current investigational tools. The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active HHV-6 infections, but the indications for treatment, as well as the conditions of drug administration, are not formally approved to date. There are still numerous pending questions about HHV-6 which should stimulate future research works on the pathophysiology, diagnosis, and therapy of this remarkable human virus.

The development of new therapies for human herpesvirus 6

Human herpesvirus 6 (HHV-6) infections are typically mild and in rare cases can result in encephalitis. A common theme among all the herpesviruses, however, is the reactivation upon immune suppression. HHV-6 commonly reactivates in transplant recipients. No therapies are approved currently for the treatment of these infections, although small studies and individual case reports have reported intermittent success with drugs such as cidofovir, ganciclovir, and foscarnet. In addition to the current experimental therapies, many other compounds have been reported to inhibit HHV-6 in cell culture with varying degrees of efficacy. Recent advances in the development of new small molecule inhibitors of HHV-6 will be reviewed with regard to their efficacy and spectrum of antiviral activity. The potential for new therapies for HHV-6 infections will also be discussed, and they will likely arise from efforts to develop broad spectrum antiviral therapies for DNA viruses.

Highlights in antiviral drug research: antivirals at the horizon

This review highlights ten "hot topics" in current antiviral research: (i) new nucleoside derivatives (i.e., PSI-352938) showing high potential as a direct antiviral against hepatitis C virus (HCV); (ii) cyclopropavir, which should be further pursued for treatment of human cytomegalovirus (HCMV) infections; (iii) North-methanocarbathymidine (N-MCT), with a N-locked conformation, showing promising activity against both α- and γ-herpesviruses; (iv) CMX001, an orally bioavailable prodrug of cidofovir with broad-spectrum activity against DNA viruses, including polyoma, adeno, herpes, and pox; (v) favipiravir, which is primarily pursued for the treatment of influenza virus infections, but also inhibits the replication of other RNA viruses, particularly (-)RNA viruses such as arena, bunya, and hanta; (vi) newly emerging antiarenaviral compounds which should be more effective (and less toxic) than the ubiquitously used ribavirin; (vii) antipicornavirus agents in clinical development (pleconaril, BTA-798, and V-073); (viii) natural products receiving increased attention as potential antiviral drugs; (ix) antivirals such as U0126 targeted at specific cellular kinase pathways [i.e., mitogen extracellular kinase (MEK)], showing activity against influenza and other viruses; and (x) two structurally unrelated compounds (i.e., LJ-001 and dUY11) with broad-spectrum activity against virtually all enveloped RNA and DNA viruses.

Human herpesvirus 6 U69 kinase phosphorylates the methylenecyclopropane nucleosides cyclopropavir, MBX 2168, and MBX 1616 to their monophosphates

Dihydroxymethyl and monohydroxymethyl methylenecyclopropane nucleosides are effective inhibitors of both variants of human herpesvirus 6 (HHV-6). We investigated involvement of HHV-6 U69 protein kinase in their mechanism of action. Phosphorylation of the dihydroxymethyl analogue cyclopropavir and monohydroxymethyl nucleosides with either a 6-ether moiety (MBX 2168) or a 6-thioether moiety (MBX 1616) with purified U69 was examined. All three compounds were substrates of this viral kinase and had similar Michaelis-Menten kinetic parameters.

Primary HHV 6 infection after liver transplantation with acute graft rejection and multi-organ failure: successful treatment with a 2.5-fold dose of cidofovir and reduction of immunosuppression

HHV type 6 has been reported with enhanced pathogenicity in immunocompromised patients. Herein, we report about a two-yr-old girl who experienced primary HHV 6 infection after liver transplantation. She clinically presented with graft rejection and necrotic hepatitis as well as high fever, pneumonitis with respiratory failure and a rash. Therapy with cidofovir of 5 mg/kg per wk did not show improvement, so that a full pharmacokinetic profile of cidofovir was performed. It demonstrated enhanced body weight normalized clearance of cidofovir and cidofovir dosage was augmented to 12 mg/kg per wk to reach adequate drug exposure. With additional reduction of immunosuppression, the patient dramatically improved and liver function stabilized.

Benzimidazole analogs inhibit human herpesvirus 6

Several benzimidazole nucleoside analogs, including 1H-β-D-ribofuranosyl-2-bromo-5,6-dichlorobenzimidazole (BDCRB) and 1H-β-L-ribofuranosyl-2-isopropylamino-5,6-dichlorobenzimidazole (maribavir [MBV]), inhibit the replication of human cytomegalovirus. Neither analog inhibited the related betaherpesvirus human herpesvirus 6 (HHV-6). Additional analogs of these compounds were evaluated against both variants of HHV-6, and two L-analogs of BDCRB had good antiviral activity against HHV-6A, as well as more modest inhibition of HHV-6B replication.

Hematopoietic cell transplantation and emerging viral infections

Viral infections remain important causes of morbidity and mortality in hematopoietic cell transplant recipients. More recent developments in preparative regimens and graft manipulations, as well as the control of well-recognized post-transplant infections by the introduction of prophylaxis and preemptive strategies, have influenced the timing and the epidemiology of infections. As new pathogens, such as human metapneumovirus (HMPV), human bocavirus, human coronaviruses HCoV-NL63 and HCoV-HKU1, human herpesviruses HHV-6 and HHV-7, and polyomaviruses, have emerged, it is fundamental to determine the significance of the newly discovered viruses and their role in the transplantation field. This article summarizes recent data on epidemiology and laboratory diagnosis of new pathogens, as well as clinical features and management of the associated infectious complications. J. Med. Virol. 82:528-538, 2010. (c) 2010 Wiley-Liss, Inc.

Human herpesvirus 6

Az 1986-ban felfedezett emberi 6-os herpeszvírus A és B változata molekuláris tulajdonságai alapján a legősibb emberi herpeszvírus. A B változat cseppfertőzéssel terjed a tünetmentes vírusürítő felnőttekről a két év alatti kisgyermekekre, akikben alkalmilag exanthema subitum jöhet létre. A vírus a CD4+ macrophagokat, lymphocytákat fertőzi, utóbbiakban élethossziglan lappangás, időnként a nyálmirigyekben vírustermeléssel járó perzisztencia alakul ki. Felnőttkorban ez a változat csontvelő- és szervátültetések kapcsán, immunszuppresszió talaján reaktiválódik, és akár halálos szövődményeket hoz létre. Sclerosis multiplex, idült fáradtság tünetegyüttes, Hodgkin- és nem Hodgkin-lymphomák kialakulásában kofaktor. A CD+-sejteket fertőző és bennük lappangó A változat közvetlen kórokozó képessége nem ismert. A HIV-fertőzést rendkívül erősen transzaktiváljain vitroés betegekben egyaránt. Papillomavírusok által okozott daganatokban is transzaktivátor. Mindkét vírusváltozat kórokozó képessége a megváltozott citokin- és kemokinegyensúlyon alapszik. A két változat elkülönítése szerológiailag nehézkes, erre a savóból vagy a fehérvérsejtekből végzett változatspecifikus PCR alkalmas. A súlyos komplikációk kezelésére, esetleg kemoprofilaxisára ganciclovir, esetleg foscarnet és cidofovir használható.

Antiviral therapy for respiratory tract infections

Viruses are important pathogens causing respiratory tract infections both in the community and health-care facility settings. They are extremely common causes of morbidity in the competent hosts and some are associated with significant mortality in the compromised individuals. With wider application of molecular techniques, novel viruses are being described and old viruses are found to have new significance in different epidemiological and clinical settings. Some of these emerging pathogens may have the potential to cause pandemics or global spread of a severe disease, as exemplified by severe acute respiratory syndrome and avian influenza. Antiviral therapy of viral respiratory infections is often unnecessary in the competent hosts because most of them are selflimiting and effective agents are not always available. In the immunocompromised individuals or for infections caused by highly pathogenic viruses, such as avian influenza viruses (AIV), antiviral treatment is highly desirable, despite the fact that many of the agents may not have undergone stringent clinical trials. In immunocompetent hosts, antiviral therapy can be stopped early because adaptive immune response can usually be mounted within 5-14 days. However, the duration of antiviral therapy in immunosuppressed hosts depends on clinical and radiological resolution, the degree and duration of immunosuppression, and therefore maintenance therapy is sometimes needed after the initial response. Immunotherapy and immunoprophylaxis appear to be promising directions for future research. Appropriate and targeted immunomodulation may play an important adjunctive role in some of these infections by limiting the extent of end-organ damage and multi-organ failure in some fulminant infections.

Antivirals: current state of the art

Most of the antiviral agents that have been approved, and are currently used in the treatment of virus infections, are targeted at HIV, HBV, herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV) and HCV or influenza virus. Additional compounds for HIV, HBV, HSV, VZV, CMV, HCV, influenza virus and several other viral infections, for example poxvirus (e.g., variola, vaccinia and monkeypox), respiratory syncytial virus, hemorrhagic fever virus (e.g., Lassa, Rift Valley and Ebola) and enterovirus (e.g., polio, Coxsackie and echo), are still in the experimental stage, that is, under clinical or preclinical development.

Antiviral activity of diverse classes of broad-acting agents and natural compounds in HHV-6-infected lymphoblasts

BACKGROUND

HHV-6 replication requires complex and poorly understood interactions between viral and cellular factors.

OBJECTIVES

Several natural compounds or broad-acting pharmacological agents were studied in an attempt to discover new targets for anti-HHV-6 therapy.

STUDY DESIGN

The antiviral activity was determined in human T-lymphoblasts, using HHV-6A (GS)-infected HSB-2 cells, HHV-6B (Z29)-infected MOLT-3 cells and HHV- 6B (HST)-infected MT4 cells. Virus replication was measured by CPE and qPCR assay. Foscarnet was included as the reference compound.

RESULTS

Among the 15 natural compounds tested, only 'red marine algae' (an extract rich in sulfated polysaccharides) exhibited strong activity when added during virus adsorption. Among the broad-acting pharmacological agents, chloroquine, artemisinin, hypericin, ribavirin, resveratrol and glycyrrhizic acid were all inactive. Amantadine produced a reproducible inhibition of HHV-6 replication, albeit at relatively high concentrations. Except for lamotrigine, which was moderately active against HHV-6B, several antiepileptic drugs were shown to have no activity. We included several compounds which we previously described as potent HHV-6 inhibitors, i.e., the non-nucleoside inhibitor CMV423 and the acyclic nucleoside phosphonate analogues cidofovir and 9-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine. The latter compound exhibited remarkable anti-HHV-6 activity.

CONCLUSION

Further optimization of compounds belonging to diverse classes of antiherpetic agents, for their specific action against HHV-6, is warranted.

Status Presens of Antiviral Drugs And Strategies: Part I: DNA Viruses and Retroviruses

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of HIV infections. The others have been approved for the therapy of herpesvirus (HSV, VZV, CMV), hepadnavirus (HBV), hepacivirus (HCV) and myxovirus (influenza, RSV) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these are targeting HIV infections. Yet, quite a number of important viral pathogens (i.e. HPV, HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.